Isolation of iodide-oxidizing bacteria from iodide-rich natural gas brines and seawaters

Iodide-oxidizing bacteria (IOB), which oxidize iodide (Gamma) to molecular iodine (I-2), were isolated from iodide-rich (63 mu M to 1.2 mM) natural gas brine waters collected from several locations. Agar media containing iodide and starch were prepared, and brine waters were spread directly on the media. The IOB, which appeared as purple colonies, were obtained from 28 of the 44 brine waters. The population sizes of IOB in the brines were 10(2) to 10(5) colony-forming units (CFU) mL(-1). However, IOB were not detected in natural seawaters and terrestrial soils (fewer than 10 CFU mL(-1) and 10(2) CFU g wet weight of soils) 1, respectively). Interestingly, after the enrichment with 1 mM iodide, IOB were found in 6 of the 8 seawaters with population sizes of 10(3) to 10(5) CFU mL(-1). 16S rDNA sequencing and phylogenetic analyses showed that the IOB strains are divided into two groups within the a-subclass of the Proteobacteria. One of the groups was phylogenetically most closely related to Roseovarius tolerans with sequence similarities between 94% and 98%. The other group was most closely related to Rhodothalassium salexigens, although the sequence similarities were relatively low (89% to 91%). The iodide-oxidizing reaction by IOB was mediated by an extracellular enzyme protein that requires oxygen. Radiotracer experiments showed that IOB produce not only I-2 but also volatile organic iodine, which were identified as diiodomethane (CH2I2) and chloroiodomethane (CH2ClI). These results indicate that at least two types of IOB are distributed in the environment, and that they are preferentially isolated in environments in which iodide levels are very high. It is possible that IOB oxidize iodide in the natural environment, and they could significantly contribute to the biogeochemical cycling of iodine.

从多个地点采集的富含碘化物（63微摩尔至1.2毫摩尔）的天然气盐水中分离出了能将碘化物（I⁻）氧化为分子碘（I₂）的碘化物氧化细菌（IOB）。制备了含有碘化物和淀粉的琼脂培养基，并将盐水直接涂布在培养基上。呈现为紫色菌落的IOB从44份盐水中的28份中获得。盐水中IOB的种群数量为每毫升10²至10⁵个菌落形成单位（CFU）。然而，在天然海水和陆地土壤中未检测到IOB（分别少于每毫升10个CFU和每克土壤湿重10²个CFU）。有趣的是，在使用1毫摩尔碘化物富集后，在8份海水的6份中发现了IOB，其种群数量为每毫升10³至10⁵个CFU。16S rDNA测序和系统发育分析表明，IOB菌株在变形菌门的α - 亚类内分为两组。其中一组在系统发育上与耐玫瑰变色菌（Roseovarius tolerans）关系最为密切，序列相似性在94%至98%之间。另一组与盐红嗜盐菌（Rhodothalassium salexigens）关系最为密切，尽管序列相似性相对较低（89%至91%）。IOB的碘化物氧化反应由一种需要氧气的胞外酶蛋白介导。放射性示踪实验表明，IOB不仅产生I₂，还产生挥发性有机碘，已鉴定为二碘甲烷（CH₂I₂）和氯碘甲烷（CH₂ClI）。这些结果表明，至少有两种类型的IOB分布在环境中，并且它们在碘化物水平非常高的环境中优先被分离出来。IOB有可能在自然环境中氧化碘化物，并且它们可能对碘的生物地球化学循环有重大贡献。